3-Dimensional ventricular electrical activation pattern assessed from a novel high-frequency electrocardiographic imaging technique: principles and clinical importance

Autocorrelation maps for optimal setting in cardiac resynchronization therapy

BACKGROUND AND OBJECTIVE

Patients with chronic heart failure are treated with implanted devices artificially stimulating the ventricular myocardium to support the ventricular activation propagation dynamics. The criterion for stimulation/pacing timing is a shortening of the QRS duration in the ECG signal. The study suggests additional ECG parameters that could be helpful in cardiac resynchronization therapy (CRT) device pacing settings.

METHODS

This issue was approached by computing and evaluating autocorrelation maps derived from body surface potential maps during the QRS complex. The autocorrelation maps were calculated from the body surface potential maps of seventeen patients, fourteen of whom were diagnosed with the left bundle branch block (LBBB) and three with the right bundle branch block (RBBB). Eleven of the LBBB patients were responders, and all three RBBB patients and three LBBB patient were non-responders. The body surface potential maps were measured during their spontaneous heart rhythm and optimal CRT setting. The patients' autocorrelation maps were compared with the autocorrelation maps of a control group of 33 healthy persons using two-sample Kolmogorov-Smirnov and Wilcoxon rank-sum statistical tests.

RESULTS

The autocorrelation maps from spontaneous rhythm were significantly different (p < 0.00008) in healthy and LBBB groups, which was shown on 19 parameters extracted from the autocorrelation maps by both the statistical tests of equality. In the optimal CRT setting in the LBBB responders, four of the studied parameters (Shannon entropy of the histogram of the autocorrelation map's values, and mean, standard deviation, and geometrical mean of the autocorrelation map's positive values) were not significantly different from the parameters of the healthy subjects (p > 0.19).

CONCLUSIONS

Selected parameters of autocorrelation maps can be used as additional parameters for optimal CRT pacing settings, leading to patients' positive responses to the treatment.

Evaluation of Non-Invasive Isochronal Late Activation Mapping in Scar Related VT with Electrocardiographic Imaging against Contact Mapping

BACKGROUND

Deceleration zones (DZ) represent important ablation targets in scar-related ventricular tachycardias (VT). Novel Electrocardiographic Imaging (ECGI) techniques could identify DZs instantly and non-invasively.

OBJECTIVE

Evaluate a novel ECGI last deflection detection algorithm for non-invasive isochronal late activation substrate mapping (iLAM) in scar-related VT procedures against electroanatomical mapping (EAM) METHODS: Prospectively recruited scar-related VT ablation patients underwent contact and ECGI mapping. SR or RV-paced baseline maps were acquired, temporal signal averaging performed and unipolar electrograms (EGM) reconstructed. Local activation time was annotated to the last negative deflection (LD) before T-wave. iLAMs were generated by dividing activation maps in 8 and 12 isochronal zones. Number and location of ECGI late activation areas (LAA) and ECGI-DZ were compared to EAM on a segmental basis.

RESULTS

47 patients (27.7% ischemic, 72.3% non-ischemic) were studied, epicardial data was acquired in 30 (63.8%). No significant difference in the absolute LAAs were identified on ECGI versus EAM (p=0.161), latest EGM was significantly later on EAM. ECGI late activation mapping yielded a sensitivity of 68% and specificity of 95%. EAM identified DZs in 91.5%, ECGI in 93.6% of patients (p 0.5). ECGI detected significant more DZs per map than EAM (2.5±1.2 vs 1.2±0.8, p <0.001) but less steep activation gradients (p 0.002). Sensitivity for ECGI-DZ mapping was 46.8%, specificity 90.6% in the context of a high number of total segments, and pre-emptive exclusion of interpolated/artificial DZ (identified in 95.7%).

CONCLUSION

ECGI with LD detects late activation zones in the majority of cases with a moderate sensitivity. Yet, detailed functional substrate mapping including accurate localisation of local DZs remains challenging with low sensitivity precluding its clinical use for this indication in its current form.

Characterizing collagen scaffold compliance with native myocardial strains using an ex-vivo cardiac model: The physio-mechanical influence of scaffold architecture and attachment method

Applied to the epicardium in-vivo, regenerative cardiac patches support the ventricular wall, reduce wall stresses, encourage ventricular wall thickening, and improve ventricular function. Scaffold engraftment, however, remains a challenge. After implantation, scaffolds are subject to the complex, time-varying, biomechanical environment of the myocardium. The mechanical capacity of engineered tissue to biomimetically deform and simultaneously support the damaged native tissue is crucial for its efficacy. To date, however, the biomechanical response of engineered tissue applied directly to live myocardium has not been characterized. In this paper, we utilize optical imaging of a Langendorff ex-vivo cardiac model to characterize the native deformation of the epicardium as well as that of attached engineered scaffolds. We utilize digital image correlation, linear strain, and 2D principal strain analysis to assess the mechanical compliance of acellular ice templated collagen scaffolds. Scaffolds had either aligned or isotropic porous architecture and were adhered directly to the live epicardial surface with either sutures or cyanoacrylate glue. We demonstrate that the biomechanical characteristics of native myocardial deformation on the epicardial surface can be reproduced by an ex-vivo cardiac model. Furthermore, we identified that scaffolds with unidirectionally aligned pores adhered with suture fixation most accurately recapitulated the deformation of the native epicardium. Our study contributes a translational characterization methodology to assess the physio-mechanical performance of engineered cardiac tissue and adds to the growing body of evidence showing that anisotropic scaffold architecture improves the functional biomimetic capacity of engineered cardiac tissue. STATEMENT OF SIGNIFICANCE: Engineered cardiac tissue offers potential for myocardial repair, but engraftment remains a challenge. In-vivo, engineered scaffolds are subject to complex biomechanical stresses and the mechanical capacity of scaffolds to biomimetically deform is critical. To date, the biomechanical response of engineered scaffolds applied to live myocardium has not been characterized. In this paper, we utilize optical imaging of an ex-vivo cardiac model to characterize the deformation of the native epicardium and scaffolds attached directly to the heart. Comparing scaffold architecture and fixation method, we demonstrate that sutured scaffolds with anisotropic pores aligned with the native alignment of the superficial myocardium best recapitulate native deformation. Our study contributes a physio-mechanical characterization methodology for cardiac tissue engineering scaffolds.

Ultra-high-frequency ECG volumetric and negative derivative epicardial ventricular electrical activation pattern

From precordial ECG leads, the conventional determination of the negative derivative of the QRS complex (ND-ECG) assesses epicardial activation. Recently we showed that ultra-high-frequency electrocardiography (UHF-ECG) determines the activation of a larger volume of the ventricular wall. We aimed to combine these two methods to investigate the potential of volumetric and epicardial ventricular activation assessment and thereby determine the transmural activation sequence. We retrospectively analyzed 390 ECG records divided into three groups-healthy subjects with normal ECG, left bundle branch block (LBBB), and right bundle branch block (RBBB) patients. Then we created UHF-ECG and ND-ECG-derived depolarization maps and computed interventricular electrical dyssynchrony. Characteristic spatio-temporal differences were found between the volumetric UHF-ECG activation patterns and epicardial ND-ECG in the Normal, LBBB, and RBBB groups, despite the overall high correlations between both methods. Interventricular electrical dyssynchrony values assessed by the ND-ECG were consistently larger than values computed by the UHF-ECG method. Noninvasively obtained UHF-ECG and ND-ECG analyses describe different ventricular dyssynchrony and the general course of ventricular depolarization. Combining both methods based on standard 12-lead ECG electrode positions allows for a more detailed analysis of volumetric and epicardial ventricular electrical activation, including the assessment of the depolarization wave direction propagation in ventricles.